This invention relates to laminated glass structures and methods for their production. More particularly it concerns high performance energy reflective laminated glass structures with improved visual appearance and improved life.
Laminated glass has been in widespread use for over fifty years. Conventional laminated glass has two or more sheets of glass fixed to one another with an intermediate layer of bondable adhesive plastic, particularly poly(vinylbutyral) (xe2x80x9cPVBxe2x80x9d). This is the conventional xe2x80x9csafety glassxe2x80x9d structure.
In some cases it is desired to incorporate an energy reflective layer into glass laminates to give a high performance product. This reflective layer can be added for light control and/or more typically for heat control with the layer serving as a heat reflector.
The energy reflective layer can be one or more thin substantially transparent layers of metal or metal oxide or combinations of metal and metal oxide or the like. Various configurations for energy reflective layers are well known in the art.
There are two methods commonly in use to produce energy-reflective high performance laminated glass. The most widely-used method is to deposit the energy-reflective layer directly on one of the glass sheets, commonly by a vacuum deposit method such as sputter deposition or by vacuum evaporation; and then add a sheet of PVB over the reflective layer followed by a top lite of glass.
This three layer sandwich is then run through a conventional heat and pressure lamination process to form a single bonded unit.
The other practice is to put the vapor-deposited coating on a flexible substrate such as PET, encapsulate this coated film between two relatively thick sheets of PVB, sandwich the PVB-film-PVB stack between two panes of glass, and then run the standard heat and pressure lamination process. Compared to putting the reflective coating directly on glass, putting coating on a flexible substrate makes it easier to manufacture in a continuous fashion. It also makes it easier to inventory reflective-coated materials before lamination and permits one to ship coated films to distant laminators. The choice of 15 mil (0.38 mm) or thicker sheets of PVB has offered two advantages. First, the PVB can be sold in pre-formed sheets. Second, the sheets of PVB provide structural properties such as fracture resistance when thick.
The use of coated film encapsulated between two sheets of 15 mil (0.38 mm) or thicker PVB for making laminated glass has been practiced commercially for many years. Coated PET and PVB are pre-laminated or are laminated during the final glass unit lamination process. The problem with this approach is that commercial sheet PVB is textured for de-airing during lamination. The texture from the PVB will emboss onto the PET. Subsequently, the reflective image from the vapor deposited coating is not planar and is objectionable. This waviness in the reflective image is referred to in the trade as xe2x80x9capplesaucexe2x80x9d. Three means on paper to minimize this effect involve 1) using PVB sheets with relatively smooth surface (U.S. Pat. No. 5,091,258 by Monsanto), 2) masking the visible effects of wrinkles in the coated film by minimizing the reflectivity of the coating (U.S. Pat. No. 4,973,511 by Monsanto), and 3) using PET with certain thermal shrink characteristic (U.S. Pat. No. 4,465,736 by Teijin). However, these prior methods have not proved to be satisfactory because xe2x80x9capplesaucexe2x80x9d is not completely eliminated. The shortcomings of these methods become very obvious when a reflective coated plastic film is used.
The use of a reflector-coated plastic film in laminated glass units has a second problem. Reflective coatings on PET are more susceptible to corrosion than similar coatings on rigid substrates. Presumably, this is due to cracking or fracturing of the coating during lamination, creating tunnels for corrosive elements to transfer through or past the thick PVB layers. To prevent such corrosion, a special reflective coating which includes gold has been employed. This adds cost. The invention described herein eliminates xe2x80x9capplesaucexe2x80x9d completely and for reasons not completely understood, substantially reduces the tendency for coatings to corrode.
We have now found a way to eliminate the optical distortion known as xe2x80x9capplesaucexe2x80x9d from laminated glass structures which include an energy-reflective coated plastic intermediate layer.
Stated most generally we have found that if we bond the coated plastic intermediate layer to one of the glass sheets using a very thin (e.g. 0.25 to 5 mil) (0.006 mm to 0.127 mm) layer of adhesive this gives a highly planar texture to the coated plastic intermediate layer. This planarity is retained when this glass-sheet-adhesive-plastic film composite is incorporated into a final laminated glass structure using a second layer of adhesive and a second sheet of glass.
In one aspect this invention provides an xe2x80x9capplesaucexe2x80x9d-free laminated glass final product. This product has a first glass sheet with a smooth first surface; a first adhesive layer affixing a plastic film to the smooth surface of the first glass sheet. This first adhesive layer is thin, that is less than 5 mils (0.127 mm) thick. The plastic film is registered and conformed to the smooth surface of the first glass sheet. The plastic film carries an energy-reflective coating. The glass laminate is completed by a second adhesive layer bonding the plastic film to a second glass sheet. The energy-reflective layer can be on either side of the plastic film but better results are achieved if it faces the thin adhesive layer and first glass sheet.
In another aspect this invention provides an intermediate to this final product. This intermediate is a plastic film carrying the energy reflective layer and a 5 mil (0.127 mm) or less coating of adhesive on either side of the film but preferably on the side carrying the energy reflective layer where it unexpectedly provides a final product having greater stability and product life with improved corrosion resistance for the energy reflective layer.
In a further aspect the invention provides a method for producing this intermediate in which an energy reflective layer coated plastic film is coated (preferably over the energy reflective coating) with a solution of an adhesive. Then the solvent is removed from the solution coating, leaving a layer of adhesive on the energy-reflective layer carrying plastic film. The thickness of the coating of adhesive solution is predetermined to yield a final neat adhesive layer that is less than 5 mils (0.127 mm) thick.
This process can be part of an overall laminated window production scheme in which the adhesive-coated, reflective layer-carrying plastic film is adhered and conformed to a smooth surface of a first sheet of glass, a second layer of adhesive is applied followed by a second sheet of glass and the overall structure is laminated.